The present invention is directed to a device having an arrangement for measuring or sensing a value of a measured condition at a test location and having an arrangement for transmitting the measure values to a remote location.
When transmitting a measured value, which is in the form of electrical signals, from the measured location to a remote location, various problems occur. Examples of these problems are that the electrical signals when transmitted, in particular, over electrical lines are sensitive to electro-magnetic radio interference and the employment of the electrical lines sometimes create problems because of safety reasons. For example the electrical signal can be influenced or distorted when transmitted through an area in which a high electrical potential difference occurs. In addition, the electrical signals being transmitted over the electrical line can create a danger of an explosion in certain areas. When a significant value is placed on a high operating safety, these above mentioned problems become of particular importance in industrial measurement techniques.
These above noted reasons speak in favor of attempting to modify the sensor technology by transmitting the measured values over optical lines particularly over light waveguides with the values being in the form of optical signals. Optical lines are insensitive to electro-magnetic radio interference and they are particularly employable given a high electrical potential differences and in areas subject to the danger of explosion. Added thereto are the light weight, small dimensions and high flexiblity of the light waveguides as well as their resistance to most agressive chemical substances. The properties of light waveguides thus are considerably significant in the practical areas.
Another advantage of the use of light waveguides is that given the presently standard impressed 20 mA signal for the measured value transmission, high voltage levels, which have a negative effect on the power pact cost because of high power requirements, are required. In addition, after traveling in line lenghts of approximatly 500 meters because of the significant line resistance, further processing of the signal will be required. In comparison thereto, light waveguides can bridge great distances because of the low attenuation from approximatly 1 dB/km through 5 dB/km.
However, problems do occur because many sensors or sensing means are active and therefore require an externally supplied electrical power for their operation. Beyond that, the amplitude as well as the chronological progression of the measured-value dependent electrical signal, for example the voltage is unsuitable for direct conversion into an optical signal in a number of sensors. Therefore, a pre-processing of the electrical signal emitted by the sensor is necessary and power must also be made available for this purpose.